The prior art comprises a production process in which the raw material used for obtaining crystals of high purity and quality is the syrup or raw crystal sugar in its several types: white crystal sugar, sugar B, sugar C (magma), VHP (very high polarization) sugar, VVHP (very, very high polarization) sugar and organic crystal sugar, or combinations between the several types of sugar and/or syrup.
The conventional process for producing raw crystal sugar from sugar cane is very well described in the literature in HONIG (1953), HUGOT (1969), MEADE & CHEN (1977), MEADE (1963) and VAN DER POEL et al. (1998). There are few variations in the conventional process of manufacturing white sugar from sugar cane in Brazil and abroad. Apart from small variations, which are inherent to the production of some special types of sugar, the unitary operations involved can be described ahead. The manually or mechanically harvested cane is sent to the mill, where it is cleaned (via a dry or wet process), then submitted to a preparation process in which it is chopped and defibered, submitted to extraction, which can be effected in multi-stage (usually 4 to 6) countercurrent mills, where the cane receives the addition of water in the last stage, provided by diffusers, not very common in Brazil.
This initial process generates the bagasse, which is sent to be burned in boilers (of medium or high pressure) to generate steam and electric energy, as well as the mixed juice, which is sent to treatment to produce sugar and alcohol.
In the combined mills, generally about 50% of the processed cane is destined to sugar manufacture and 50% to the production of alcohol.
The juice destined to the production of alcohol undergoes specific physical-chemical treatment and is sent to the fermentation vessels, jointly with the exhausted final run-off syrup (mother liquor) resulting from the production of sugar.
The mixed juice destined to sugar manufacture is submitted to an operation of separating the bagacillo in cush-cush type screen (and/or rotary screens) is heated to about 40° C. and conveyed to the sulfitation step (usually in columns or hydro-ejectors) where, by addition of sulfur dioxide resulting from sulfur burning in the burners, has its pH reduced to about 4.0- to 4.5. After sulfitation, the juice receives the addition of lime milk (or calcium saccharate), where the pH is elevated to about 7.0-7.2. The limed (or dosed) juice is then heated to about 105° C., and subsequently undergoes a vaporization process (“flash balloon”) for removing dissolved gases, receives the addition of a flocculating agent (usually a polyacrylamide polyelectrolyte), being then submitted to decantation in static decanters (with or without trays). This operation is also commonly known as clarification. Two streams result from the clarification process: a sludge stream and a clarified juice stream. The sludge, after being added with bagacillo (a type of “natural filtrating means”), receives the addition of lime milk and, eventually, polyelectrolyte, and is then filtrated in vacuum rotary filters or belt press filters, thus giving rise to the filter cake, which is used in agriculture, as well as the filtrated juice, which is re-conducted to the process. The obtained clarified juice is sent to evaporation in multiple effect vacuum evaporators (usually Robert type evaporators with 4 or 5 stages), yielding a concentrate juice known as syrup, with a concentration of about 65° Brix. In the first evaporation stage, normally denominated pre-evaporation, a vapor bleeding is effected to utilize said vapor in the operations of evaporation-crystallization, of heating the mixed juice and of distillation in the production of alcohol.
The syrup obtained in the evaporation is conveyed to the subsequent crystallization step, which is carried out in vacuum calendar type evaporating crystallizers in systems with two or three masses. Generally, the conventional crystallization process takes from 3 to 5 hours, and the crystal mass thus obtained is conveyed to horizontal crystallizers provided with a cooling jacket, until reaching the ambient temperature. The final mass is then submitted to a centrifugation cycle, in basket centrifuges, in which the crystals are washed upon application of water and steam and then conducted to the drying and bagging steps. The run-off syrup obtained in the centrifugation is re-used in the cooking operations for obtaining the second sugar (sugar B or magma) and, eventually, the third sugar (sugar C or magma), which are also re-circulated in the first sugar manufacturing process.
The process of producing VHP and VVHP sugar is practically the same as that employed in the production of white crystal sugar, with the difference that, for producing VHP, the sulfitation process is not used. In the VVHP producing process, besides not using sulfitation, there is eventually provided correction of the phosphate levels of the juice, and the syrup receives the addition of α-amylase and/or dextranase for hydrolyzation of the starch and dextran, respectively, when necessary.
The process for making organic sugar is practically the same as that employed in the production of the white crystal sugar, with the difference that chemical inputs are not used in the processing thereof, and that both the cultivation of sugar cane and the sugar production process follow principles of self-sustainability.
In the present process, the syrup, the solutions obtained from the dissolution of raw sugar (white crystal sugar, VHP sugar, VVHP sugar, VVHPC sugar, sugar B, sugar C, and organic sugar) in water, and mixtures thereof, which are the raw material used, will be generically denominated herein as sugar solution.
Before proceeding to the detailed description of the object of the present invention, it is important to present the several possibilities of effecting the sucrose crystallization, as described below.
There are basically three ways of carrying out the crystallization: by isothermal evaporation, by flash evaporation or by cooling. In all these forms, the objective is to start from the undersaturated zone, in which crystals are not present, and proceed until the metastable zone, in which occurs the formation and growth of crystals.
In the isothermal evaporation process, the solution is evaporated, maintaining a constant temperature of the vapor phase until the crystals have been obtained. In the flash evaporation system, the solvent is removed from the solution by evaporation effected under variable pressure, normally by means of vacuum and associated with temperature reduction. And, finally, the crystallization by cooling is carried out, starting with a saturated solution at a higher temperature, which is successfully cooled to a metastable zone for obtaining the crystal growth, therefore without evaporation.
Independently of the way used for carrying out the crystallization, the quality of the crystals obtained regarding aspects such as uniformity of granulometric distribution, color, purity, gloss and morphology of the crystals are intimately correlated with crystallization kinetics. An extense bibliographic list treats this matter in details, for example Van der Poel (VAN DER POEL, P. H., SCHIWECK, H., SCHWARTZ, T., Sugar Technology: Beet and Cane Sugar Manufacture, Dr. Albert Bartens, Berlin, 1998), Van Hook (VAN HOOK, W. A., MANTOVANI, G., MATHALOUTHI, M., Sucrose Crystallization—Science and Technology. Dr. Albert Bartens, Berlin, 1997), Mersmann (MERSMANN, A.—Crystallization Technology Handbook, Marcel Dekker, Inc, 1995), Mantelatto (MANTELATTO, P. E.—Study on the process for the crystallization of impure sucrose solutions of sugar cane by cooling, Master Degree thesis-(PPG-EQ/UFSCAR), 2005), Nyvlt (NÝVLT, J., SÖHNEL, O.; MATUCHOVÁ, M.; BROUL, M.; The Kinetics of Industrial Crystallization, Prague Academy, 1985), Giulietti (NÝVLT, J., Hostomský, J., Giulietti, M.: Crystallization, São Paulo, Brazil, IPT/UFSCar, 2001). Knowledge on the crystallization kinetics and its perfect control has been a long imperative desire in all crystallizer projects. Several authors have demonstrated that, by controlling the crystallization kinetics, it is possible to obtain high levels of removal of color, ashes, starch, dextran and reducing sugars. For example, Mantelatto (MANTELATTO, P. E.—Study on the process for crystallization of impure sucrose solutions of sugar cane by cooling, Master Degree Thesis-(PPG-EQ/UFSCAR), 2005), in which crystallization by cooling was carried out in batches, by agitation in a 10 L crystallizer, on the laboratory bench, obtaining the following results: sugar crystals having a color of 14 IU, starting from VVHP sugar having an original color of 310 IU; of 56 IU from VHP sugar with original color of 1040 IU; and of 22 IU from VHP sugar having an original color of 846 IU. It is also pointed out that the crystals obtained presented an excellent variation coefficient, VC, between 6.9% (best case) and 28% (worst case), proving the distribution is very uniform and little dispersed, mainly in the case where seeding was used. Moreover, the process proved to be effective in the removal of impurities, such as starch and ashes, obtaining, for determined cooling rates, a removal index very close to 100%.
In sugar manufacture, there are several types of equipment employed, according to the purity of the mass under crystallization process. For mass A, of high purity, for example 85 to 92%, most equipment used are of the batch vacuum evaporating crystallizers type provided with a steam-heated calendar. For mass B, with intermediate impurity, for example between 72 and 75%, are used the same batch equipment as that employed for mass A, as well as multi-compartment horizontal continuous evaporating crystallizers, horizontal batch evaporating crystallizers of the cascade type and vertical batch evaporating crystallizers of the cascade type. For mass C, the batch models can be used, identical to those used for masses A and B, multi-compartment horizontal continuous evaporating crystallizers, and also horizontal batch evaporating crystallizers of the cascade type, and vertical batch evaporating crystallizers of the cascade type. All these models and applications thereof are very well described in the literature, for example, in Van der Poel (VAN DER POEL, P. H., SCHIWECK, H., SCHWARTZ, T., Sugar Technology: Beet and Cane Sugar Manufacture, Dr. Albert Bartens, Berlin, 1998) and Hugot (HUGOT, E., Sugar Engineering Manual, Translated by MIOCQUE, I., Vol. 1 and Vol. 2, Mestre Jou Publishing Co., São Paulo-SP, Brazil, 1969).
As related in literature and also from industrial practice, the continuous crystallization processes are successfully applied in crystallizers of low and medium purity mass, for intermediate sugars B and C. For mass A (high purity), although several manufacturers propose the use of the horizontal continuous evaporating crystallizers or vertical evaporating crystallizers of the cascade type, which have been only used for crystallizing masses of low purity or intermediate purity, in practice, it is verified that the quality of the sugar thus obtained is still very bad. In this type of application, one can verify a strong formation of incrustation, agglomeration of crystals, bad crystal distribution curve (high variation coefficient), and even incorporation of color in the crystals by occlusion and inclusion, besides degradation of reducing sugars.